Process for producing micro-mesoporous metal oxide having regulated pores formed by novel template removal method

ABSTRACT

The present invention is the method for preparation of transition metal oxide having micro-mesoporous structure whose average fine pores size is not less than 1 nm and not more than 2 nm comprising, adding and dissolving transition metal salt which is a precursor of transition metal oxide and/or metal alkoxide in the solution prepared by dissolving polymer surfactant in organic solvent, hydrolyzing said transition metal salt and/or metal alkoxide and preparing sol solution which is polymerized and self organized, then obtaining gel whose organization is stabilized from said sol solution and removing said polymer surfactant by using water of room temperature or water to which alkali metal or alkaline earth metal ion is added.

FIELD OF THE INVENTION

The present invention relates to a process for producing themicro-mesoporous metal oxide having average pore size of not more than 2nm and not less than 1 nm by preparing fine pore structure of metaloxide using nonionic surfactant as a template through self-assemblingprocess by sol-gel method and removing the template from theself-assembled material using water.

DESCRIPTION OF THE PRIOR ART

It is known that nonionic surfactant assembles silica to have variousmesoporous framework structures by means of electrostatic force,hydrogen bond, covalent bond and van der Walls interaction. However, thepore wall of mesoporous silica, which is produced using the surfactantas a template, is amorphous and has a problem of stability, especiallyhigh hydrothermal stability. In such a circumstances, since the trial toapply above mentioned process for producing mesoporous structure tonon-silica oxide was attempted and tentatively succeeded, this trial iscurrently expanded to the trial to produce the mesoporous materialswhich utilize the special property such as electronic conductivity andmagnetic interaction. As the example of said materials, metal oxide suchas TiO₂, ZrO₂, Al₂O₃, Nb₂O₅, Ta₂O₅, WO₃, HfO₂, SnO₂ and metal oxideincluding mixed oxide such as SiAO_(3.5), Si₂AlO_(5.5), SiTiO₄, ZrTiO₄,Al₂TiO₅ and ZrW₂O₈ can be mentioned. Further, there is a paper reportingthat the mesoporous wall formed by said materials is different from thatof amorphous silica and is thermally stable and having relatively largepores with periodicity, for example, pores of 3 nm-14 nm, which can bebroadly utilized, can be obtained (NATURE, vol 396, 152-155 (1998):Document A).

According to the investigation by the inventors of the presentinvention, the fine pore wall made of metal oxide mentioned above withmesoporous structure is amorphous. On the contrary, the inventors of thepresent invention have already proposed the mesoporous structuralmaterial with pore wall made of crystalline metal oxide, which isimproved the disadvantage depicted above of known meso size made ofmetal oxide (Japanese Patent Laid open publication 2001-354419 filed onDec. 25, 2001 B).

However, in said prior art, the template method is use at the synthesisof mesoporous silica and mesoporous metal oxide. In the template method,template is removed by baking or acid treatment after formation ofmesoporous structure and net work of inorganic phase by self-assembling.This method is disadvantageous when estimated from the view point ofcost, safety and environmental maintenance and has problems at thesubstantive industrial application. On the contrary, the mesoporousmetal oxide is expected to be applied to the materials such as catalyst,sensor or semiconductor, and the cost reduction for production is also avery important subject. Further, in the case of zeolite, which is atypical micro porous material, since it has very fine pores of less than1 nm, there is a limitation to be applied as the selective reaction orseparation of molecule having bigger size than said fine pores, such asaromatic compound. Furthermore, in the case of the reported synthesizedmesoporous material up to the present time, since the pore size of finepores is relatively too large, there is a disadvantageous that shaperecognizing function is not easily generated, when reaction orseparation of the molecules of the size of 2 nm around.

In Japanese Patent Laid Open Publication 1997-294931 (published on Nov.18, 1997; Document C), porous material having autonomous humidityconditioning function prepared by following method is disclosed, thatis, surrounding surfactant or organic compound having long chain alkylgroup with silica dioxide or oxide of transition metal and polymerized,then by removing said organic compound by baking or extracting.

In [0007] of Document C, there is a description of “In the presentinvention, a template agent is used to obtain uniform fine pores ofaround 5 nm. As the surfactant to be used as a template can be listedthe surfactant represented by general formula RN⁺(R¹ ₃)₃.X⁻ (R: alkylgroup, R¹: methyl or ethyl group, X: halogen such as chlorine orbromine) or R(OCH₂CH₂)_(m)OH (R: alkyl group). As the specific exampleof said surfactant, decyltrimethyl ammonium bromide,dodecyltrimethylammonium bromide, tetradecyl trimethylammonium bromidehexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride,poly(oxyethylene)decylether, poly(oxyethylene)hexadecylether can belisted.”

In [0009] of Document C, there is a description of “The porous materialhaving autonomous humidity conditioning function of the presentinvention can be obtained by surrounding organic compound by oxide oftransition metal and polymerized, then by removing the organic compoundby baking or extracting.

Further, in [0009] of Document C, there is a description of “Afterdrying, in order to remove the template of organic compound, the organiccompound is extracted by organic solvent such as methanol, acetone,toluene, xylene or benzene at the temperature lower than 200° C. for notless than 3 hours or by heat treatment under presence of air at500-1000° C., for 4-10 hours retention time.

In above mentioned circumference, it is difficult for the organicmolecule with the size of aromatic compound mentioned above to bereacted or extracted selectively by using the conventional porousmaterial, and actually, the synthesis of inorganic material with finepores of around 1 nm is attempting. However, many results are reportedwhich reports that the synthesis of inorganic material having fine porewith intermediate size is difficult (S. A. Bagshaw and A. R. Haymann,Adv. Mater., 13 (2001) 1011, Document C). Therefore, it is verysignificant to provide the process for producing the metal oxide withfine pores of around 1 nm.

That is, basically, the subject of the present invention is to dissolvethe problems of maintenance of environment and production cost, and toprovide a method for preparation of mesoporous metal oxide material withnovel fine pore structure and internal surface of fine pore, inparticular with more small fine pore size, further, the subject of thepresent invention is to provide a method which is able to producemesoporous metal oxide material having desired and smaller pore sizesuitable for the use.

To dissolve above mentioned subjects, on investigating about themesoporous structure by self assembling process and a process forproducing mesoporous metal oxide material with fine pores structurereflecting the preparation of mesoporous metal oxide precursor at theformation of inorganic phase net work and/or mesoporous structure ofsaid precursor, the inventors of the present invention has found outthat by removing the surfactant which acts an important role to formfine pores at the process for forming said precursor, especially,nonionic surfactant which can be removed by water, by washing withwater, said mesoporous metal oxide can be obtained, and solved thesubject of the present invention.

SUMMARY OF THE INVENTION

The present invention is a process for producing the transition metaloxide with micro-mesoporous structure whose average pores size is notless than 1 nm and not more than 2 nm comprising, adding and dissolvingtransition metal salt which is a precursor of metal oxide and/or metalalkoxide in the solution prepared by dissolving polymer surfactant inorganic solvent, hydrolyzing said transition metal salt and/or metalalkoxide and preparing sol solution which is polymerized and selfassembled, then obtaining gel whose organization is stabilized from saidsol solution and removing said polymer surfactant by using water of roomtemperature or water to which alkali metal or alkaline earth metal ionis added.

Desirably, the present invention is the process for producing thetransition metal oxide having micro-mesoporous structure, wherein saidpolymer surfactant is the nonionic surfactant having polyalkyleneoxideblock copolymer frame, for example, nonionic surfactant comprising blockcopolymer composed of polyethylene oxide chain (CH₂CH₂O)_(m) andpolypropylene oxide chain [CH₂CH(CH₃)O]_(n) (wherein, m and n is 10-70and end of said polymer is etherized by H, alcohol or phenol). Moredesirably the present invention is the method for preparation oftransition metal oxide, wherein said process to obtain stabilized gelcontains 2nd step aging process which is carried out under the presenceof oxygen gas at 60° C. to 140° C. for 12-48 hours after gelating thesol solution to gel by primary aging process under the presence ofoxygen gas at 35° C. to 60° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the X-ray diffracting pattern of micro-mesoporous niobiumoxide obtained in Example 1, A shows the first step aging process ofgelation by aging sol solution obtained by self assembling in air at 35°C. to 60° C. for 2 to 10 days, B, C and D show relatively the cases ofstabilized state of fine pores wall structure of 2nd step aging at 60°C., 80° C. and 100° C. for 12-48 hours.

FIG. 2 shows the N₂ absorption isotherm curve of micro-mesoporousniobium oxide obtained in Example 1, A shows the case ofmicro-mesoporous product obtained by removing template by washing withwater according to the present invention, while B shows the case ofmicro-mesoporous product obtained by removing template by bakingaccording to the conventional technique.

FIG. 3 shows the X-ray diffracting pattern of micro-mesoporousmagnesium-tantalum oxide whose average pores size is 2 nm and BETspecific surface area is 210 m²/g obtained by aging of micro-mesoporousmagnesium-tantalum oxide of Example 2 at 40° C. for 2-10 days, thenfurther aged secondary at 100° C. for 24 hours.

FIG. 4 shows the N₂ absorption isotherm curve of micro-mesoporousmagnesium-tantalum oxide of Example 2.

FIG. 5 shows the N₂ absorption isotherm curve of micro-mesoporoustantalum oxide whose average fine pores size is 1 nm and surface area(BET specific surface area is 120 m²/g) obtained by aging ofmicro-mesoporous tantalum oxide of Example 3 at 40° C. for one week,then further aging secondary at 100° C. for one day.

DESCRIPTION OF THE PREFERRED EMBOBYMENT

The present invention will be illustrated more in detail.

A. As the metal which composes transition metal oxide with mesoporousstructure of the present invention is at least one selected from thegroup consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb,Mo, Ru, Cd, In, Sn, Sb, Hf, Ta, W and Re, and can be selected properlyaccording to the use of the metal oxide with mesoporous structure. Forexample, zinc oxide or complex oxide obtained by the method of thepresent invention can be predicted to be useful as the catalyst forreaction of isomerization of epoxide, and titania or vanadium oxide canbe predicted to be useful for the partial oxidation reaction of liquidphase. It was already known that the micro-mesoporous structureindicates specific catalytic property or absorption property correspondto the inorganic constitution or electric•magnetic•photo property,therefore, the known arts can be adopted for the selection of thematerial used for the preparation of the micro-mesoporous structure ofthe present invention.

B. At the preparation of the transition metal oxide with mesoporousstructure of the present invention, it is important to use the templatematerial which are actually removable by water or water to which isadded small amount of additives such as alkali metal or alkali earthmetal ion.

This is clearly understood by considering the average fine pore size ofthe mesoporous structure of the conventional arts mentioned above whichis obtained by removing organic compound template by baking at thetemperature of 300° C. or more is in the range of 2-6 nm.

C. Further characteristic of the present invention is that themesoporous structure transition metal oxide whose fine pores structureis stabilized can be obtained only by removing the template material bywater, in other words, without crystalline stabilization of fine porewall by heat treatment. That is, in the production of micro-mesoporousstructured transition metal oxide precursor before removal of saidtemplate, it is contrived to obtain mesoporous structured transitionmetal oxide whose fine pore structure is stabilized by carrying out 2ndstep aging under the presence of oxygen gas at 60° C. to 140° C. for12-48 hours on the gel obtained by aging under the presence of oxygen at35° C. to 60° C.

D. In the present invention, as the surfactant, one or more knownsurfactants can be used in combination. The mixing ratio of surfactant,transition metal salt and/or metal alkoxide and water in reactionprocess is very important factor to form an ordered fine pore structure.And by adjusting the ratio, it is possible to control the structure ofthe fine pore, for example, hexagonal structure or cubic structure.

As the surfactant, nonionic surfactant comprising block copolymer(including oligomer) composed of polyethylene oxide chain (CH₂CH₂O)_(m)and polypropylene oxide chain [CH₂CH(CH₃)O]_(n) (wherein, m and n is10-70 and end of said polymer is etherized by H, alcohol or phenol) isdesirable.

E. As the organic solvent, alcohols, for example, methanol, butanol,propanol, hexanol or mixture composed of two or more of them aredesirable.

EXAMPLE

The present invention is illustrated more specifically according to theExamples, however, not intending to limit the scope of the presentinvention.

The characteristics of the obtained micro-mesoporous oxide are measuredaccording to the following methods.

1. XRD (product of Rigaku Co., Ltd., RINT 2100, CuKα ray) method: X raydiffraction method: By lower angle (1-6°) peak pattern, periodicstructure of fine meso pores can be observed.

2. Nitrogen absorption isothermal curve (product of Coulter Co., Ltd.SA3100): Relative pressure (P/P₀) (X axis) range, where nitrogenabsorption (Y axis/volume (mL/g)) steeply increases, corresponds withthe length(diameter) of fine pore. The degree of rising relates to finepore volume.

Example 1

10 wt % of ethanol solution of nonionic surfactant composed ofpolyethylene oxide chain (CH_(2 CH) ₂O)_(m) and polypropylene oxidechain [CH₂CH(CH₃)O]_(n) (wherein, m and n is 10-70 and end of saidpolymer is etherized by H, alcohol or phenol) was prepared. 0.005-0.01mole of niobium chloride was added to 10 g of said surfactant andstirred for 20-60 minutes and dissolved. At said process, 0.5-2 mL ofwater containing 0.05M of alkali or alkali earth ion was added toaccelerate hydrolysis of inorganic compound and self-assembling. The1^(st) step aging was carried out on obtained sol solution in air at 35°C. to 60° C. for 2-10 days and A of FIG. 1 was obtained. The 2^(nd) stepaging was carried out on the obtained gel to stabilize the structure at60° C. (FIG. 2B), 80° C. (FIG. 2C) and 100° C. (FIG. 2D) for 12-48hours. Obtained gel after 2^(nd) step aging was washed with 0.1-1 Lwater per 1 g of said gel and filtrated, and said nonionic surfactant,which is the template, was removed. Sediment of removed template wasdried and at least a part of the template was reused. The material fromwhich template was removed was dried in air for several hours and thedesired micro-mesoporous niobium oxide was obtained.

Characteristics of obtained micro-mesoporous niobium oxide by saidproducing process are shown as follows.

X-ray diffraction: From the X-ray diffraction peak of FIG. 1, theexistence of fine pores structure and periodic structure correspondingto the peak angle in the specimen is confirmed.

By 2 steps aging, peaks are confirmed at nearby 1.3° and 2°, and theexistence of highly ordered fine pores structure is confirmed. For thecomparison, micro-mesoporous niobium oxide without 2nd step aging isindicated by A.

The micro-mesoporous niobium oxide obtained as above is confirmed fromX-ray diffraction pattern that the average diameter is 1.7 nm (80% offine pores are concentrated in the range of 1.7 nm±0.7 nm and reflectingthe structure which orderly arrayed by average 6 nm interval. While, thediameter of fine pore of mesoporous niobium oxide obtained by removingthe template by calcination is 5 nm.

N₂ gas absorption; from ascend feature of N₂ gas adsorption isothermcurve uniformity of fine pores can be observed and from the adsorptionamount (BET surface area), surface area and pore volume can be observed.

From N₂ gas adsorption isotherm curve of the product obtained by 2 stepsaging shown in FIG. 2 (2 steps aging at 100° C.), it is understood thatthe radius of fine pore is 1.7 nm and small, and from the ascend featureit is understood that the product has uniform fine pores. Further, it isconfirmed that the surface area of the product is 360 m²/g and is thehigh surface area product.

By the way, the surface area of mesoporous niobium oxide B obtained byremoving the template by calcination is 210 m²/g.

Further, although the obtained mesoporous niobium oxide B was not passedthe calcinating process, the stability of fine pores is good.

In the case of mesoporous niobium oxide which is obtained using themesoporous niobium oxide precursor which does not carry out 2 stepsaging, since the mesoporous niobium oxide does not have such excellentstability, it is understood that the 2 steps aging of the presentinvention is essential.

Example 2

Production of micro-mesoporous magnesium-tantalum oxide 0.003 mol ofMgCl₂ and 0.07 mol of TaCl₅ were poured into 10 wt % of P-123 [Tradename, product of BASF:(HO(CH₂CH₂O)₂₀(CH₂CH(CH₂)O)₇₀(CH₂CH₂O)₂₀)H]/propnol solution. Afterreacted for 30 minutes, aged at 40° C. for 2-10 days, then 2^(nd) stepaging was carried out at 100° C. for 24 hours. Template was removed bywashing with water, and micro-mesoporous magnesium-tantalum oxide of 2nm average pore size and 210 m²/g specific surface area was obtained.

X-ray diffraction curve is shown in FIG. 3 and N₂ gas adsorptionisotherm curve is shown in FIG. 4. In FIG. 4, A is the micro-mesoporousmagnesium-tantalum oxide produced by the process for producing of themicro-mesoporous composition of the present invention. While, B is themicro-mesoporous magnesium-tantalum oxide prepared by removing templateby calcination, and the average pore size of this micro-mesoporousmagnesium-tantalum oxide is 6 nm and BET specific surface area is 114m²/g.

Example 3

Micro-Mesoporous Tantalum Oxide

0.07 mol of TaCl₅ was poured into 10 wt % of P-123 [product name,product of BASF: (HO(CH₂CH₂O)₂₀(CH₂CH(CH₂)O)₇₀(CH₂CH₂O)₂₀)H]/propanolsolution. After reacted for 30 minutes, aged at 40° C. for 1 week, then2^(nd) step aging was carried out at 100° C. for 1 day. Template wasremoved by washing by 1 L of water, and micro-mesoporous tantalum oxidewas obtained.

Average pore size of fine pore of the obtained micro-mesoporous tantalumoxide was 1 nm and surface area (BHT specific surface area) is 120 m²/g.By the way, the average pore size of fine pore of the mesoporoustantalum oxide prepared by removing template by calcination is 3 nm.

In FIG. 5, N₂ gas adsorption isotherm curve of the obtainedmicro-mesoporous tantalum oxide is shown.

INDUSTRIAL APPLICABILITY

As mentioned above, by the process for producing the transition metaloxide having micro-mesoporous structure of the present invention, thefollowing excellent effect can be provided. That is, the transitionmetal oxide of micro-mesoporous structure having fine pore of around 1nm, which can not be obtained by the conventional technique, and thestability-improved fine pore wall can be obtained by using templatebeing able to be removed by washing with water, which is very economicaland harmless to the environment can be easily prepared.

1. A method for preparation of transition metal oxide havingmicro-mesoporous structure whose average fine pore size is not less than1 nm and not more than 2 nm comprising, adding and dissolving transitionmetal salt which is a precursor of transition metal oxide and/or metalalkoxide in the solution prepared by dissolving polymer surfactant inorganic solvent, hydrolyzing, polymerizing and self-assembled thetransition metal salt and/or metal alkoxide to produce sol solution, andthen obtaining framework-stabihzed gel from the sol solution, andremoving the polymer surfactant by using water or water to which alkalimetal or alkaline earth metal ion is added at room temperature.
 2. Themethod for preparation of transition metal oxide having micro-mesoporousstructure of claim 1, wherein surface area of transition metal oxidehaving mesoporous structure is from 100 m²/g to 500 m²/g.
 3. The methodfor preparation of transition metal oxide having micro-mesoporousstructure of claim 1, wherein the process to obtain the stabilized gelcontains 2nd step aging process which is carried out under the presenceof oxygen gas at 60° C. to 140° C. for 12-48 hours on the gel obtainedby gelating the sol solution to gel by aging under the presence ofoxygen gas at 35° C. to 60° C.
 4. The method for preparation oftransition metal oxide having micro-mesoporous structure of claim 3,wherein surface area of transition metal oxide having micro-mesoporousstructure is from 100 m²/g to 500 m²/g.
 5. The method for preparation oftransition metal oxide having micro-mesoporous structure of claim 1,wherein polymer surfactant is a nonionic surfactant havingpolyalkyleneoxide block copolymer frame.
 6. The method for preparationof transition metal oxide having micro-mesoporous structure of claim 5,wherein the process to obtain the stabilized gel contains 2nd step agingprocess which is carried out under the presence of oxygen gas at 60° C.to 140° C. for 12-48 hours on the gel obtained by gelating the solsolution to gel by aging under the presence of oxygen gas at 35° C. to60° C.
 7. The method for preparation of transition metal oxide havingmesoporous structure of claim 6, wherein surface area of transitionmetal oxide having micro-mesoporous structure is from 100 m²/g to 500m²/g.